Abstract Number: PB0571
Meeting: ISTH 2020 Congress
Background: The antifactor Xa heparin assay (anti-Xa) and the activated partial thromboplastin time (aPTT) are commonly used to monitor the anticoagulant effects of unfractionated heparin (UFH).
Aims: The purpose of this study is to examine the relationship between the values of anti-Xa and aPTT, simultaneously collected, to monitor UFH infusion.
Methods: This single-center, retrospective and observational study uses anti-Xa and aPTT values from patients in a Brazilian University Hospital gathered from 2018 to 2019. We analyzed 506 paired values from 52 patients. Therapeutic range for anti-Xa was 0.3- 0.7 IU/mL and values > 0.7 IU/mL were considered supratherapeutic. The aPTT based heparin therapeutic range was calculated on laboratory using regression analysis: Therapeutic range for aPTT was defined as 60-80 s and values > 80s were considered supratherapeutic. Results with decreased level of antithrombin (AT) III were excluded.
Results: From 506, we evaluated 441 values, where 65 (13%) values met the exclusion criteria were decreased level of ATIII (36 ±8 mg/dL). For the 194 antiXa values in the therapeutic range, aPTT values were in subtherapeutic range (< 60 s) for 67 samples (35%) and in supratherapeutic range (>80 s) for 30 samples (15%). Only 97 samples (50%) were in aPTT therapeutic range (60-80 s). For 246 anti-Xa values in subtherapeutic range, 187 (76%) resulted in aPTT values < 60 s, for 41 (17%) aPTT values were between 60-80 s and for 18 (7%) aPTT values were >80s. There was one supratherapeutic anti-Xa levels (0.8 IU/mL), in agreement with an aPTT>80s. This patient had no bleeding episodes on the medical records.
|Total (n=441)||Terapeuthic range (Total: 194), n (%)||Subtherapeutic range (Total=246), n (%)||Supratherapeutc range (Total=1), n (%)|
|aPTT <60s||67 (35%)||187(76%)||–|
|aPTT : 60 to 80s||97 (50%)||41(17%)||–|
|aPTT >80s||30 (15%)||18(7%)||1|
|activated partial thromboplastin time (aPTT)|
[Number of samples of Antifactor Xa and activated partial thromboplastin time on the therapeutic range]
Conclusions: Anti-Xa therapeutic range and APTT values are discordant in 97 samples which represent 50% of total samples, presenting to 67 samples aPTT values lower and for 30 samples higher than expected considering the anti-Xa values.
To cite this abstract in AMA style:Silva VM, Cavalheiro C, Strunz CC. Antifactor Xa Levels vs. Activated Partial Thromboplastin Time for Monitoring Unfractionated Heparin [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/antifactor-xa-levels-vs-activated-partial-thromboplastin-time-for-monitoring-unfractionated-heparin/. Accessed November 26, 2020.
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